2.9.1
Upper Course
In
the upper course,
- The
river channel is small,
narrow and rough and
usually shallow.
- The
stones and rocks
increase wetted
perimeter.
- The
volume of water is low
as there are very few
tributaries flowing into
it.
2.9.1.1
Interlocking Spurs
[fig 2.9.1(a)]
Interlocking
spurs are alternate hills in
the river valley. The river
does not have a high water
volume at this point and
even though it is fast
flowing, the river cannot
laterally erode (sideways)
to remove the spurs. Because
of this, the river has to
flow around the spurs,
eroding vertically.
Fig
2.9.1(a)
2.9.1.2
Potholes
[fig 2.9.1(b)]
As
the river is vertically
eroding in the Upper Course,
potholes can be created when
larger pieces of load that
the river cannot remove by
traction are twisted around
by eddy currents. The river
is not strong enough here to
pull the large boulder in
the diagram, and the
obstruction creates a
swirling motion in the
water. Eventually, the
boulder creates a pothole,
by abrasion on the river
bed.
Fig
2.9.1(b)
2.9.1.3
Waterfalls and Gorges
[fig 2.9.1(c & d)]
In
the Upper Course, the river
is not only eroding
vertically (down) but
towards its source (HEADWARD
EROSION). This means the
feature shown in the diagram
above is created. The river
erodes the softer rock
underneath the harder rock
on top faster, and this
means the level of the land
along the river's course
becomes lower over time and
the waterfall retreats back
towards the source.
Successive positions of the
waterfall are shown on the
diagram. The movement
backwards leaves a second
feature called a GORGE.
Fig 2.9.1(c)
Looking
at a side view, the process
becomes clearer. Splash back
from the falling water
erodes away the softer rock
faster, leaving the hard
rock without support and it
collapses into the plunge
pool. The process then
repeats itself, with the
waterfall further towards
the source of the river.
Fig
2.9.1(d)
